Typically, all of the specs are on the company's website. Look for first hour delivery rate, and recovery rates. You can get an idea if you want to do some math...a gallon of water is approximatley 8 pounds. If you figure the flow rate in gallons/minute, you can get the weight of the water you want to heat. Then figure how many degrees it needs to raise the temp. A BTU is one pound/one degree (typically) per hour. A BTU/minute = 17.569W. So 3 gallons/minute = 24 pounds. If you need to raise it from 50 degrees to 110, that's 60 degrees. 60*24*17.569 = 25,299W. The thing is probably only about 2-3 Kw, so the water you used in one minute would take about 12-13 minutes to reheat. I haven't double-checked my math, but I think I'm right. Since you are mixing the cold water with what is already there, it will just continually get cooler until you are barely raising the temp once all of the stored water is diluted with the incoming.